Dark Side
by Nisbet
Summary: Dean was never rescued from hell and became a demon while Sammy on earth goes dark-side, Ruby still at his side. The demon brothers reunite to take down earth. The angels try to stop them and fail. Only Castiel is able to reach through to Dean.


**"Dean was never rescued from hell and became a demon while Sammy on earth goes dark-side, Ruby still at his side. The demon brothers reunite to take down earth, the angels try to stop them and fail, only Castiel is able to reach through to Dean."**

* * *

"Dean."

He looked up from the small, lanky man named Garth cowering before him and his focus snapped to the intruder who'd arrived with a small gust of wind and the flap of invisible wings. Castiel. One of the more... _humane_ angels in his garrison. Dean had seen him in all of his trench-coated glory before when he and Sam were fighting their way out of an angel-infested graveyard a few weeks ago.

"Just a minute, Hesediel," he said, his gaze returning to the hunter, "I'm in the middle of something." He knew Castiel wouldn't attack. At least not yet. He wasn't the type to immediately throw punches upon arrival.

The angel clenched his jaw. "It's _Cas_tiel," he said. Dean's lips twitched up in amusement.

"All right, angel," he replied with a wink, the smirk on his face lacing his tone with sarcasm. Dean grinned at Garth who was shaking in the seat he was tied to. The wooden legs of the chair rattled faintly against the concrete floor of the basement they were in. "So this is what Bobby brings in to replace us," Dean purred, his voice dangerously gentle, "a scruffy kid who doesn't look any more threatening than a puppy. Pathetic. You'd think Singer would have more competent-looking people on speed dial."

Sam stepped out of the shadows and into the light that was cast by the single naked bulb hanging over their heads. "Whatever happened to Rufus?" he asked with only mild interest. "We were expecting him and Bobby—instead, we got you."

"Ru-Rufus is dead," Garth stammered, blinking sweat out of his eyes. His fingers were working at the knots behind his back, but Dean was confident the kid would never untie them. It was a knot he'd learned a long time ago. "Your girl over there killed him," Garth said, his chin jerking to the left slightly, indicating somewhere behind him.

"Did I?" The voice came from the opposite side of the room where Ruby had been reclined in a folding chair, hidden in a darkened corner. She re-crossed her legs and folded her arms in front of her chest, unimpressed. "Well, you kill so many humans, it's hard to keep track."

"_Dean_. Sam." The angel was trying to get their attention again.

"Shut him up, Sammy," Dean said, not taking his eyes away from Garth. "Tell him he needs to schedule an appointment, or he can haul his feathery ass upstairs until I can give him my undivided attention."

Sam raised his hand and his eyes swirled with black, clouding any innocence the amber irises appeared to once have held. His fingers curled around thin air and, out of the corner of Dean's eye, he could see Castiel fall to his knees with his hands grasping at his neck. A bright light was inside the angel's throat—his Grace. Sam could pull it right out of him in a second, but he was keeping it concentrated in his esophagus, forcing him to choke on his own essence. Sam was getting creative.

"Where were we, Garthy boy?" Dean asked the trembling hunter. "Oh, right. We need some info on Bobby Singer."

Garth gritted his teeth. "Good luck getting anything from me," he said bravely. Cute.

"Uh-huh," Dean said, bored. "Look, whether or not you agree to it or not, we're going to find out where he's holed himself up for the time being, and what cell number he gave you to contact him with. Not the one that's programmed into your disposable phone," he said, making sure Garth knew he wasn't screwing around, "the one you have memorized."

"How'd you—"

"C'mon, kid, we worked with Bobby before. We know how the guy thinks." Dean tapped his temple with the blade of the knife he'd pulled out of the back pocket of his jeans as he addressed Bobby's newest hunter. He stepped forward and, behind him, Castiel made a particularly loud choking noise. Nobody bothered to watch him suffer—even Sam's eyes were on the kid.

"So you have three seconds to decide whether or not you want this to go quickly," Ruby said. She stood up from her seat and joined Sam and Dean in front of Garth, her hands on her hips. "I don't have two hours to waste on someone like you," she said scornfully.

Sam looked at her and checked an imaginary watch on his wrist. "Do you really think it'll take that long? I said I'd be back in Hell for that backgammon tournament between Crowley and the hellhound housebreakers."

Dean let himself smile. "We'd just have to be real careful in order to make it last—I mean, look at that delicate frame."

"We could start with his fingers," Ruby said. She put a hand on Garth's shoulder and he shuddered at the contact. "Peel back the skin from bone and— _OW!_" She had pressed her palm to his face and pulled away with a screech of pain. She was clutching her hand to her chest. "_Holy water_," she snarled.

Garth's lips tilted up and he dropped his petrified act. "Right. Spritzed myself with it before I came in." His voice was strong and sure and didn't break as it had before. He suddenly pushed himself over backward in the chair and rolled out from under the harsh light of the bulb. His hands were no longer bound behind his back and he was up and moving around freely. Dean made to go after him, but was stopped by an invisible force. He looked up.

Devil's trap.

A piece of chalk fell to the ground and everyone's eyes flew to Castiel. He'd used telekinesis to manipulate a length of chalk to draw the symbol on the ceiling while he was choking on his Grace. The guy had balls, Dean had to admit. But that didn't mean he wasn't still a huge pain in the ass.

Dean shook his head and clicked his tongue at Castiel. "Bad move, man."

"Dean, you must listen to me— There's a prophecy," the angel said desperately.

He narrowed his eyes at Castiel. "What do you mean 'a prophecy'? You mean, like, from _God_? Newsflash, buddy—"

"It says only you can save your brother," Castiel went on. "Only _you_ can reclaim his mind and tear him from the darkness the demon blood has cast on him," he said.

Dean laughed. "And why would I do that, sunshine? Because I'm _so_ good? _Look at me_. I'm a hundred percent demon, baby. I ain't a hunter no more."

"You are _still_ good. I can see it in you," Castiel pleaded, "there is light in your heart.

"You became a demon to protect Sam. Demons do not make petty bargains with their makers in order to save a fellow. Demons do not _have_ fellows. Only enemies. You love your brother, and demons are not capable of love."

Dean's smile disappeared and his lips twisted into a snarl. "You shut your holy mouth about my brother, d'you hear?"

"Remember what it was like to be human," Castiel demanded, his blue eyes imploring. "Do you remember sacrificing everything for Sam's happiness? You suffered _years_ of hardship for him and you endured hateful words from your father all for the sake of your brother—so he could have everything that you never had. You love him with all of your heart, and that love is what called the angels onto the battlefield. We believe in that love. Use it, Dean. Use it to see past the veil that Hell has draped over your eyes."

Dean gritted his teeth and clenched his fist. His mind was presenting him with memories: the fireworks in the field, the time he gave Sam the last bit of Lucky Charms, the multiple occasions when Dad had yelled at him for letting Sammy go—for making him soft…

"Dean? Dean." That was Sammy. That was him. Dean's brother. Concern was in Sam's voice as he tried to get through to Dean, reminding Dean how they much had cared for each other. "We're here. This is real. _We're_ real," Sam said. "Don't listen to the angel." Dean could barely hear him.

Sammy was the reason he did this; he'd needed a way to protect Sam, and becoming a demon was the only way Dean had known how to help him. He _did_ love his brother, there was no doubt. Why was he causing so much pain, though? What was the point to the destruction?

Something within Dean gripped him tight and squeezed his soul, wringing out the black ink Hell had tattooed him with. The pain was worse than his 600-year torture. It shot through his body and left a scorching imprint of his gruesome, demon past in his veins, but purified him. It cleansed him. It steadied him.

His eyes cleared and Castiel marveled at how they were no longer coal pieces in his skull. They were human. Dean's fists relaxed and his knees gave out. He fell to the floor with a gasp. Castiel caught Dean before he could collapse and Dean balanced on his knees, bleary-eyed and trying to find his center of gravity. Castiel's hand pressed against Dean's cheek and sent a wave of warmth throughout Dean's body to comfort him.

The human looked up, blinking against the illumination of the naked bulb eclipsed by Castiel's head, the ring of light around him a corporeal version of a halo. He touched the angel's hand that was holding the side of his face, making sure that he was real.

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**This is my first Supernatural fic, so please give me feedback!**


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